The present invention relates generally to lighting apparatus, and more particularly provides a uniquely constructed heat-dissipating light fixture for use with tungsten-halogen lamps.
The vast majority of lights currently used in retail and exhibition display applications are incandescent flood lamps which range in power from 100 watts to 300 watts. Despite the prevalence of its use, incandescent display lighting is subject to several well known disadvantages and limitations. For example, the efficiency of incandescent lamps is limited to approximately eight to eleven percent, which results in high electrical power consumption compared to the useful light obtained. Additionally, the spectrum of the light generated by incandescent display lamps is heavily weighted toward the infrared portion of the spectrum. This results in relatively poor color balance of the displayed objects.
Moreover, heat that is generated by the infrared component of incandescent display lamps is projected forwardly, thereby potentially creating undesirably high temperatures on the illuminated merchandise. This last point is particularly relevant where bright lighting is required for expensive or irreplacable objects such as clothing, furs, jewelry, or paintings. It is well known that concentrated infrared energy can significantly deteriorate the object at which it is directed. As an example, infrared energy can change the molecular structure of diamonds and other precious stones, thereby significantly decreasing their value. Additionally, watches are particularly sensitive to heat, and are easily damaged under incandescent lighting.
As an alternative to high wattage, low efficiency incandescent lighting, dichroic, tungsten-halogen low voltage lamps have recently been utilized in display applications and potentially offer several distinct advantages over incandescent lighting systems. For example, the efficiency of tungsten-halogen low voltage lamps is approximately ten times that of incandescent lamps. At 12 volts, a 75 watt tungsten-halogen lamp produces essentially the same amount of usable light as a much higher wattage incandescent lamp, and produces more of the light output in the visible spectrum. This, of course, represents a significant energy savings. Additionally, the life of a tungsten-halogen lamp is approximately 2.5 to 3 times that of an incandescent lamp due to the "halogen cycle" which redeposits evaporated tungsten on the lamp's filament, preventing blackening of the lamp envelope and also prolonging the life of the tungsten filament.
The color spectrum of the light produced by tungsten-halogen lamps provides a truer color representation for illuminated objects due in part to the high "white hot" temperature that the tungsten filiment is heated to, and to the special dichroic coating on the lamp reflector which reflects visible light and absorbs other transmitted frequencies such as infrared. Finally, projected heat from a tungsten-halogen lamp is significantly reduced by its dichroic reflector which absorbs approximately 70 percent of the infrared radiation (as well as ultraviolet) resulting in a safe light for illuminating delicate merchandise.
It can be seen that these advantages inherent in tungsten-halogen lamps make them a very desirable light source for many retail and other commercial applications. However, the conventional fixtures in which these tungsten-halogen lamps are typically housed significantly shorten the useful life of such lamps. This is due primarily to the inability of conventional fixtures to adequately dissipate the intense heat produced at the rear of the lamp by the high temperature tungsten filament and by the reflector-absorbed infrared energy. A typical method of installing a tungsten-halogen lamp in the conventional light fixture is simply to plug the connecting prongs of the lamp into a connector fitting disposed within the fixture. Other than allowing the heat from the lamp base portion to be somewhat dissipated by convective transfer to air within the fixture surrounding the lamp, no adequate heat dissipation mechanism has heretofore been incorporated in these fixtures.
This deficiency in conventional fixture design leads to premature lamp failure in three primary modes due to excessive heat buildup in the lamp. First, the seal portion of the lamp often fails, thereby allowing the halogen gas within the glass envelope to escape, due to interior seal temperatures exceeding 350.degree. C. The lamp seal is typically made of electrically conductive strips such as molybdenum, pressed between the quartz envelope. Due to the high filament temperature and high current (6.25 amps at 75 w) flowing through the strips they often reach very high temperatures. Additionally, if the reflector temperature is allowed to exceed approximately 350.degree. C., the reflector's dichroic coating can deteriorate. Finally, the connector fitting within the fixture can also be caused to fail due to the high temperature transmitted from the lamp base to the connector pins. Excessively high temperature can result in increasing resistance and eventual breakdown of the connector pin and of the power supply connection thereto.
It can be seen from the foregoing that a need exists for an improved light fixture for use with tungsten-halogen lamps which eliminates or substantially minimizes above-mentioned and other lamp heat buildup problems and limitations. Accordingly, it is an object of the present invention to provide such a fixture together with associated lamp heat-dissipating methods.